The present invention relates to a solenoid valve for controlling a fuel injector for an internal combustion engine.
A solenoid valve is discussed in German Published Patent Application No. 196 50 865 which is used to control the fuel pressure in the control pressure space of a fuel injector, e.g., an injector of a common rail injection system, where the fuel pressure in the control pressure space in turn controls the movement of a valve member, so that an injection opening of the injector may be opened or closed. This solenoid valve has an electromagnet situated in a housing part and having a coil and a magnetic core, a movable armature and a control valve element that is moved with the armature and is acted upon by a closing spring in the closing direction. This control valve element cooperates with a valve seat of the solenoid valve and thus controls the flow of fuel out of the control pressure space. In the case of the solenoid valve discussed in German Published Patent Application No. 196 50 865, the armature is designed in two parts having a foundation bolt and an anchor plate in a slidingly displaceable mount on the foundation bolt. In addition, however, there are solenoid valves for controlling injectors in which the foundation bolt is fixedly connected to the anchor plate.
One disadvantage of the known solenoid valves is armature rebound. When the magnet is shut down, the control valve element, which is secured to the armature, is accelerated suddenly toward the valve seat by the closing spring to close a fuel outflow channel out of the control pressure space. The impact of the control valve element on the valve seat may result in vibration and/or rebound of the control valve element, which is a disadvantage and has a negative impact on the injection operation. In the case of the solenoid valve having a two-part armature, which is discussed in German Published Patent Application No. 196 50 865, rebound is prevented by the fact that the anchor plate is displaceable on the foundation bolt and is moved further against the tension force of a restoring spring in impact of the control valve element on the valve seat. The effectively braked mass thus becomes smaller. However, then it is necessary to prevent post-pulse oscillation of the anchor plate on the foundation bolt, which would be a disadvantage. This is achieved by a hydraulic damping space formed between a sliding sleeve secured on the anchor plate and a sliding piece situated in a stationary mount on the housing part of the solenoid valve, damping any post-pulse oscillation of the anchor plate. In the case of a very strong deflection of the anchor plate in the direction of closing of the control valve element, the anchor plate strikes against the sliding piece situated in a stationary mount in the housing part. Any residual pulse is transferred to the stationary sliding piece and from there to the housing part.
The solenoid valve according to an exemplary embodiment of the present invention may be situated on a slidingly displaceable part on the foundation bolt, the part being displaceable between two stops, both of which may be fixedly situated on the foundation bolt. On impact of the control valve element with the valve seat, the slidingly displaceable part may move in the direction of closing of the control valve element against the tension force of the restoring spring, like the anchor plate in the case of the solenoid valve from the related art. The mass of the slidingly displaceable part and the tension force of the restoring spring may be designed so that the slidingly displaceable part may strike against the second stop of the foundation bolt. Since this second stop is not fixedly mounted on the housing, but instead may be movable with the armature and may be secured on it, rebound of the armature from the valve seat may be reduced by the transfer of momentum of the slidingly displaceable part to the foundation bolt. This may be possible because the momentum of the armature rebounding on the valve seat and the momentum of the lagging, displaceable part on the foundation bolt may be directed in opposing directions. The present invention may also be used to advantage with such solenoid valves in which the anchor plate may be designed in one piece with the foundation bolt, thus preventing post-pulse oscillation of the anchor plate. By reducing the rebound and post-pulse oscillation of the control valve element on the valve seat, it may advantageously be possible to set shorter intervals between preinjection and the main injection, because the armature may take less time to assume a defined rest position.
The second stop formed on the foundation bolt may be formed to advantage by a ring surface, facing the slidingly displaceable part, of a hollow cylindrical sleeve fixedly connected to and displaced on the foundation bolt. In assembly, the displaceable part may be pushed onto the foundation bolt first and then the sleeve may be pushed onto it.
The first stop opposite the second stop for the displaceable part may be formed in a simple manner by a ring shoulder on the foundation bolt between the anchor plate and the second stop.
The slidingly displaceable part may advantageously include a sleeve-shaped base body pushed onto the foundation bolt and having on its end facing the first stop a flange on which the restoring spring is supported.
The mass of the slidingly displaceable part may correspond approximately to the mass of the armature formed by the anchor plate and the foundation bolt and this may result in the momentum of the displaceable part being approximately the same as that of the armature rebounding on the valve seat.
The present invention may be applied with solenoid valves using a one-part armature having an anchor plate secured on the foundation bolt or using a two-part armature having an anchor plate displaceable relative to the foundation bolt. In the latter case, the anchor plate may then be provided as the slidingly displaceable part which strikes against the second stop of the foundation bolt in the closed position of the solenoid valve.